Antenna arrays with many antenna ports are part of a promising technology with many potential applications in wireless communication. Such antenna arrays are for example relevant in current 4G and future 5G systems which are based on Orthogonal Frequency Division Multiplexing (OFDM) or variants thereof, such as for instance Single-Carrier Frequency Division Multiple Access (SC-FDMA).
A typical linear or planar antenna array consists of many closely spaced antennas, each antenna comprising a number of antenna elements. Because of the close spacing, signals received at neighboring antennas are often highly correlated. Likewise, samples of the received signal which are closely spaced in the frequency domain are also often highly correlated.
If the number of antenna ports increases, while maintaining the number of antenna elements constant, the Signal to Noise Ratio (SNR) in each antenna port of the antenna array decreases due to loss in antenna array gain. This in turn entails a degradation of channel estimates, which is a key for obtaining good uplink (UL) performance. Also, increasing both the number of antenna elements and antenna ports makes it possible to receive weaker signals as more signal energy can be collected, but the channel estimate has to be maintained accurate; else the use of more antennas will not improve the user experience. There is thus a need for improving channel estimates for large antenna arrays, having a large number of closely spaced antennas.